1. Field of the Invention
The invention relates generally to protocol analyzers and more particularly to a protocol analyzer and method for selecting and recording multi-directional communication packet traffic in a compact manner in realtime while maintaining relative times precisely between the selected packets passing in one direction and the selected packets passing in another direction.
2. Description of the Prior Art
Digital devices communicate by sending electronic signals through a physical transmission channel according to a specified protocol. The protocol describes the manner in which the signals are sent and defines the detailed rules that govern both the channel and the device hardware and software. The channel and the protocol are both typically specified by a formal communication protocol specification. For transmissions to be successful, each device must recognize and follow the same specification.
Most recent protocol standards are based on packets. This means that data is transmitted in discrete packets instead of continuously. A packet is defined as a discrete quantity of data organized into a bundle for transmission. Packets typically contain data that acts as a start delimiter, data that acts as an end delimiter, and data in the middle. The data in the middle includes headers, information intended for an end user, and error detection or correction data.
Protocol analyzers have been developed to store (record) communication traffic and aid in its analysis. For proper analysis the recorded traffic must indicate the order in which it was received. Because the physical channel may be idle for a significant portion of time, it is highly desirable to store a compact record by recording data only during times when the channel is actually carrying traffic. It is also desirable for a user to set parameters so that packets with certain characteristics are recorded and others are ignored. For a single channel by itself, it is relatively straightforward to detect non-idle time, select certain desired packets and record the selected packets in time order. However, it is more difficult to achieve this performance when it is necessary to record traffic from two or more channels simultaneously because the elimination of the idle time and the purging of unneeded packets for each channel causes the time alignment between the channels to be lost. Existing techniques record al time periods and then eliminate the idle time and unneeded packets with post processing. Unfortunately, these techniques can only be used for short periods of time because the size of the recording memory required for long time periods is too large to be practical and/or economical.
There is a need for a multi-channel protocol analyzer and method for making compact time-aligned records of selected packets.